Tania Mukherjee Department of Earth And Atmospheric Sciences University of Houston April 28, 2010 Near-surface geophysical imaging in a highly structured area, Beartooth Mountains, Montana

Content Introduction to the geology and motive of the survey Acquisition and instrumentation Well log (Gamma,SP, resistivity,sonic, acoustic televiewer,neutron porosity) VSP (simultaneous three component near offset VSP in two borehole) Surface seismic (2D seismic line ) Gravity ( two perpendicular gravity profile near borehole) Interpretation Core samples Well log VSP Surface seismic Gravity Conclusion Future work Acknowledgement

N Simplified statigraphy ( Kauffman et al.(2008) Geology of Beartooth,Montana

Survey Layout YBRA CAMP Gravity profile 1 YB 1 YB2 Seismic line Gravity profile 2 Tear Zone Index Borehole Gravity profile Seismic line Tear Fault

Data acquisition (well logging) Logging cable winch Tripod stand Well  Following logs has been run in YB1 and YB2 Natural gamma, Spontaneous Potential Resistivity, Full wave sonic, Acoustic televiewer Neutron porosity.  Century geophysical Students log the wells along with field instructors. Well 2

Data acquisition VSP 3-C Downhole Geophone Geostuff Data Collector Geostuff Digitizer Inverter VSP recording cables Source Trigger Cable VSP source, 10 lb hammer No of well2 (YB1 &YB2) Cemented and cased (PVC) Location of the wellsYBRA camp Distance between wells 6.3 m Well depthYb1 :30 m, Yb2 :60 m Type of sensor3 component down-hole locking geophone. Recording unitDell Tough book laptop Sampler and digitizerGeostuff and geode Controller softwareSeismodule by Geometrics Sampling interval0.5 ms Record length1.0 s Source10 lb Hammer Shot location3.77 m from YB2 Vertical Seismic Profiling was conducted simultaneously in two wells. VSP geometry

Data acquisition (surface seismic) Propelled Energy Generator Data Recorder [Geometrics Stratavisor] Vertical planted Oyo Geophone Survey line Line Location YBRA camp near 70 m from well 2 ( camp location:45°11’15”N 109°14’55” ) Line orientationE-W No of geophone 48 vertical geophones Source100 lb accelerated weight drop Recording unitStratavisor Geophone interval 3 m Source interval3 m (between geophones) Sampling0.25ms Record length1.0 s No of shots/station 4 Raw Data

YB1 Processing and Interpretation Lithology interpretation from cuttings The wells were drilled with a water-well rig by Douglas Drilling using compressed air. Cutting samples were collected every 5 ft. From the cuttings, the first 7m is interpreted to be regolith (landslide, colluvium, and pediment deposits). At 7m (22 ft), carbonates were encountered (possibly Mississippian Madison limestone), At 40m (122 ft), a red bed was entered (unconformable Amsden formation or the later Triassic Chugwater formation). 40 m 7 m

Processing and Interpretation ( Well logs ) YB1 YB2 Carbonate Shale Carbonate Shale

Well log (Televiewer) Processing and Interpretations Caliper GammaAmp Caliper GammaAmp Dipping beds Fracture

Processing and Interpretations (VSP) Raw vertical component VSP from YB1.Two simultaneous run are plotted together for comparison of repeatability Frequency and amplitude spectrum of vertical component VSP if YB1. The dominant frequency is Hz. Raw vertical component VSP from YB2. Frequency and amplitude spectrum of vertical component VSP of YB2. The dominant frequency is Hz. P and S wave velocity inversion from first break peaks (YB2). First breaks plot for P First breaks plot for S Average velocity (P) Average velocity (S) Internal velocity (P) Internal velocity (S) First breaks plot for S P and S wave velocity inversion from first break peaks (YB1). First breaks plot for P Average velocity (P) Average velocity (S) Internal velocity (P) Internal velocity (S)

Processing and Interpretation Comparison of computed velocities and Vp/Vs plots from surface Waves (MASW method) and VSP. Vp from MASW and VSPVs from MASW and VSP MASW by S. Roy Vp from MASW Vp from VSP Vs from VSP Vs from MASW m m

High density to low density Processing and Interpretation (gravity)

2D line near well YB 2 Processing and Interpretation (gravity) O.Omoboya

Conclusion The carbonate (Madison LS?) shows a lower velocity (2600 m/s) than the competent shale beneath(2800 m/s). The high gamma ray count in carbonate indicates radioactive impurities. There is a highly fractured zone at about 130 ft (39m). The petrophysical and seismic evidence indicate the transition from carbonate to red shale occurs around 40 m. The dip of the formation is about 40-45° towards the south. Near-surface velocities from surface seismic MSAW and VSP are repetitively consistent. Processed 2D line shows no structure (parallel to fault ). A Vp / Vs value of 2.2 for the limestone and 1.7 for the shaley unit.

Future work Allied Geophysical Lab, University of Houston. GEDCO and IonGXT. Dr.Robert R. Stewart (University of Houston ). Dr. Christopher Liner (University of Houston ). Dr.Stewart Hall (University of Houston). Dr. Joe Wong (University of Calgary). Graduate students Zimin Zhang, S. Roy and O.Omoboya Acknowledgement Multi azimuth and Walkaway VSP. 2D seismic line perpendicular to the present line. Core sample analysis by geologist. Well log correlation to find out vertical shift between two wells.

Thank you